ISOless sensors, read noise and photography - many questions!

Started Oct 3, 2013 | Discussions thread
RussellInCincinnati
Senior MemberPosts: 3,197
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underexposure's post-processing burden barely worth mentioning
In reply to boardsy, Oct 30, 2013

original poster boardsy wrote: ...if the sensor is effectively ISOless then is base ISO always optimal ...or are you as well off raising it in camera (providing highlights are preserved) rather than in RAW/pp?

Russell: Well have finally brought that concept into the field. In the scene below, the flight was going to be at ISO 3200 and 1/10th of a second. Around F/8 to get complete cross-frame clarity. Everything looked fine in the electronic viewfinder (i.e. clip-on eyepiece-magnified LCD).

But then remembered at the last minute "hey, why sweat the exact exposure when I'm worried about blowing out highlights in the white fabrics? Why worry about how many bracketing exposures needed, at what intervals, just in case? Why not move the ISO back to 800, the screen looks kind of dark but everything's still perfectly viewable/manual focusable, and then can have the luxury of deciding in post-processing exactly how bright to raise the scene highlights?

This is an interesting result Russell - did you need to handle noise carefully in LR or just use defaults?

There was no careful anything. The only thing I did to handle the "underexposed" image taken with cam set to ISO 800 above, was spend somewhere between 3 and 10 seconds moving the normally-little-used "exposure" slider in Lightroom 4.x to the right, to about +1.88 EV or whatever.

After doing that, there wasn't the slightest difference or extra trouble involving unusual noise suppression or anything else. Well the difference was it was kind of fun to feel absolutely zero stress about having blown highlights in an unbracketed scene with lots of high-key detail, the God-like comfort of just moving the exposure slider as little or as much as wanted until the highlights were just shy of burning out.

I'd still wonder about ""the same" or better results by post-processing an image from a camera set to ISO 800" - if the same, why bother (unless of course to preserve crucial highlights, as above!), if better to "do ISO in pp" then it's worth the trouble to focus and frame with a dim LCD...

Firstly, it's only in the electronic viewfinder era that we have the possibility of seeing an image at the "right" brightness. You and I have been looking at optical viewfinders for years, where the brightness of the previewed image has been arbitrarily darker or brighter than/irrelevant to the final print. So it's not exactly like a fresh outrage that the electronic image preview is a couple of stops darker than the final print.

On a more complex note, we can break all scenes in the world down into 2 categories. Scenes that have nothing bright in them at all, and scenes that do. The scenes that have nothing bright in them at all, you can just set the cam to ISO 3200 with impunity, heck you could set the ISO too high if you felt like it, since we just said the scene has nothing bright in at all to blow out. The scenes that do have something bright in them, well at least the bright parts of the scene (which visually are usually the most important) are easily discernible in an EVF, even if you're underexposing by a couple of f-stops.

It's not like everything disappears just because you're 2 stops dark. Let's also recall that in a near-ISO-less cam like a Nex, you only need to leave the viewfinder a stop or two dark, just dark enough that there is no possibility of blowing highlights. If I have an ISO 3200 scene, it's quite fun to set the ISO to 800, because that's just a huge safety margin, the 2-stop-under relieves me from bracketing, with no troublesome penalty in post-processing. And since I'm only 2 stops under, the view isn't so bad. After all don't typical scenes have 8-12 stops or more of dynamic range? 2 stops is really a hill of beans most of the time.

hmmm... this may be a NEX-specific issue, but maybe use a raised flash to trigger the always-bright LCD, and block the flash (hood, or whatever) from influencing the exposure?

Am intending for this discussion to apply to users of any raw-capable camera.

In the specific Nex case, it's only miserly folks like me who are happy to work with $225 dollar used Nex x3x bodies, who don't have access to a menu setting for always-bright finder. This whole issue of dark finders dries up and blows away for Nex 5+ cams that have a permanent setting for always-bright finder. Hmm but then doesn't that mess up the on-screen histogram?

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